Senaka Basnayake

1. Characteristics of severe thunderstorms over Bangladesh and neighborhood: Observations & WRF-ARW model simulations Senaka Basnayake Asian Disaster Preparedness Centre Thailand WRF Lecture Series, 20 – 24 September 2010 @ BCCR - Norway

3. “Safer communities and sustainable developmentthrough disaster risk reduction”

4. History of ADPC Established in 1986, at the initiative of WMO, UNDP and UNOCHA Served as the Outreach Center of Asian Institute of Technology, 1986-1999 Independent international foundation, July 1999 Inter-governmental charter signed, February 2005 Over 100 staffs,19 nationalities

5. ADPC Organization Chart Board of Trustees 23 Members 16 Countries International Advisory Council (IAC) 95 members Regional Consultative Committee (RCC) 32 Members 26 Countries Executive Committee Office of the Executive Director (OED) Climate Risk Management (CRM) Urban Disaster Risk Management (UDRM) Public Health in Emergencies (PHE) Disaster Management Systems (DMS) Training Resource Group (TRG)

6. Severe thunderstorms or Nor’westers

7. Favorable Synoptic conditions for Nor’westers • Presence of an active elongated trough of low over the Gangetic plains of north India across north Bangladesh on the mean seal level pressure chart • Presence of southerly low level jet with a pole ward meridional component in the lower tropospheric wind flow • High magnitude of moisture in the humidity field intruding from the Bay of Bengal into Bangladesh and thereafter north India • Presence of sub-tropical jet stream with strong vertical wind shear in the low to middle troposphere levels over Bangladesh and neighborhood • Intrusion of high convective available potential energy (CAPE) from the Bay of Bengal into Bangladesh and presence of a low convective inhibition energy (CINE) regime. • A pocket of strong warm temperature advection at 850 hpa and cold temperature advection at 300 hpa

9. 2009 pre-monsoon

10. 2009 pre-monsoon season

11. 2009 pre-monsoon season N (10) (29) NW NE (9 8) W E (3) (4) SW SE (2) S (3) 41 – 60 km/h ~ 41, 61 – 90 km/h ~ 27, 91 – 120 km/h ~ 2

12. Week instability CAPE < 1000 J/kg Moderate instability 1000 J/kg < CAPE < 2500 J/kg Strong instability CAPE > 2500 J/kg Threshold Value >1500 0 > (NEGATIVE) CAPE CINE Very Stable atmospheric condition LI ≥ 6.0 Stable condition - unlikely to form thunderstorms 1.0 < LI < 6.0 Slightly Unstable - possible thunderstorms with mechanical lifting -2.0 < LI < 0.0 Unstable - likely to form thunderstorms with strong mechanical lifting -6.0< LI < -2.0 Very Unstable - likely to form severe thunderstorms with strong mechanical lifting LI < -6.0 Possible showers or thunderstorms SI ≤ +3.0 Possible severe convective activity SI ≤ -3.0 SI LI

13. TTI SWEAT Indicator of occurrence of thunderstorm TTI ≥ 40 Indicator of occurrence of thunderstorm with tornado intensity TTI ≥ 47 Indicator for potential strong convection SWEAT = +250 Indicator for potential severe thunderstorms SWEAT = +300 ndicator for potential tornados SWEAT = +400 Thunderstorms unlikely due to too much wind shear BRN < 10 Possibility of Supercells 10 < BRN < 45 Storms with multicells than supercells BRN > 45 BRN

15. (d) (e) (f)

17. Weather Research and Forecasting (WRF) • Developed by the Mesoscale and Microscale Meteorology Division of National Centre for Atmospheric Research (NCAR) of USA • National Centre for Environment Prediction (NCEP) real time analysis (FNL) data as initial and lateral boundary conditions (LBCs) at six hourly intervals • Domain parameters & Model physics; • Horizontal Resolution : 9 km • No. of grid point along X : 153 • No. of grid point along Y : 139 • No. of Vertical sigma levels : 27 • Iterative Time step : 50 seconds • Integration scheme : 3rd order Runga-Kutta • mp_physics : WSM 3 • Cumulus parameterization : Kain-Fritch scheme • Sf_sfclay_physics : Monin-Obukhov with • Carslon-Bolan viscous sub-layer option • Sf_surface_physics : Noah LSM • ra_lw_physics : RRTM • ra_sw_physics : Dudhia • Boundary layer parameterization : Yonsei University scheme

27. Composite Characteristics

28. Concluding Remarks…. • Convective indices at Patna, Ranchi, Guwahati and Agartala stations are good indicators for identifying possible thunderstorm days over Bangladesh as the systems initiate or conceive over West Bengal, Assam and Meghalaya regions. • Some of the factors which are essential for triggering of Nor’westers such as low level moist southerly jet from the head Bay of Bengal, mid-trophospheric cold dry westerly trough, etc. are well simulated by the model. • WRF-ARW model is able to simulate some salient features of thunderstorms with some temporal and spatial shifting.

29. Acknowledgement • SAARC Meteorological Research Centre (SMRC) • Bangladesh Meteorological Department (BMD) • Dr. Someshwar Das and research team at SMRC

30. Tusen Takk

31. Mission • raising awareness and enhancing knowledge and skills ------------------------------------------------------------------------- • strengthening sustainable institutional mechanisms ------------------------------------------------------------------------- • facilitating exchange of information, experience and expertise ------------------------------------------------------------------------- • developing and demonstrating innovative disaster risk reduction practices

32. Goals • Mainstream Disaster Reduction in Development • Build and Strengthen Capacity • Facilitate Partnerships and Exchange of Experiences • Be recognized as a Proactive and ResponsiveRegional Resource • Achieve Quality Service Through a Team Approach

33. ADPC Highlights ADPC Projects and Programs: • Longest serving regional center globally • Proactiveand responsive regional resource center • 81 projects and programs across Asia • Regional Early Warning Center provides services to 27 countries in the region